The present invention relates to a developing device for a copier, facsimile apparatus, printer or similar image forming apparatus and, more particularly, to, in a developing device of the type having a developing chamber and a removable toner container storing toner to be replenished into the chamber, an improvement in the mounting and dismounting procedure of the container and an improvement in the replenishment of the toner from the container into a hopper.
Conventional developing devices having a single developing chamber include one which allows a toner container, storing toner to be replenished into the chamber, to be slid into or out of the device body. This kind of device is taught in, for example, Japanese Utility Model Laid-Open Publication No. 2-78962 and will be referred to as Prior Art 1.
Another conventional device having a single developing chamber is constructed such that a toner container is mounted to the mount portion of the device body and then rotated in the mount portion to bring a toner outlet thereof into alignment with a toner inlet formed in the mount portion. This kind of device will be referred to as Prior Art 2.
Japanese Patent Laid-Open Publication No. 3-2883, for example, discloses a developer supply device having a hollow cylindrical developer container. The container is provided with a developer outlet and a drive connecting portion at one end of its circumferential wall. An axial spiral groove is formed in the inner periphery of the container. The developer is conveyed to a developing section along a preselected path by conveying means. A holding portion supports the container inserted thereinto and includes a receptacle portion for guiding the developer from the developer outlet to the preselected path. A drive section delivers a torque to the container inserted in the holding portion by way of the drive connecting portion. This device will be referred to as Prior Art 3.
A developing device having a plurality of developing chambers is also conventional and applicable to a full-color image forming apparatus of the type exposing an image carrier with color-separated image light, developing the resulting latent images by toner of colors complementary to the separated colors, and then transferring toner images to a single paper one above the other. This kind of device will be referred to as Prior Art 4. The developing chambers may be arranged in parallel around the image carrier as independent units. Alternatively, the developing chambers may be arranged at preselected circumferential positions in a rotary support facing the image carrier. The rotary support, or revolver, is rotatable to sequentially move its chambers to a developing position where the image carrier is located. The revolver is made up of a rotary developing unit, a rotary toner storing unit, and toner conveying means. The developing unit is rotatable in the vicinity of a photoconductive drum, or image carrier, and has a plurality of developing chambers thereinside. The storing unit is coaxially provided on one end of the developing unit. A plurality of storing chambers are defined in the storing unit in one-to-one correspondence with the developing chambers, and each stores toner of particular color. Each storing chamber is communicated to one of the developing chambers by the conveying means. For this kind of revolver, a reference may be made to, for example, Japanese patent Laid-Open Publication Nos. 62-251772 and 63-78170, and Japanese Utility Model Laid-Open Publication No. 63-41164.
There has also been proposed a revolver similar to the above-described type of revolver except that a plurality of hopper portions are substituted for the storing chambers and connected to the associated developing chambers by respective toner conveying means. A toner container storing toner of particular color is removably mounted to a toner inlet formed in each hopper portion. The hopper portions are affixed to the base plate of the developing unit, and each has its edge portion configured as a mount portion for mounting the container. The mount portion and the edge portion allow the container to be slid into or out of the hopper portion in the axial direction of the developing unit. This revolver will be referred to as Prior Art 5.
Prior Art 5 also proposes to form at the center of the developing unit a bore open at the toner storing unit side, and to store black toner, which is used most often, in a hollow cylindrical container having a greater capacity than color toner containers. The black container is mounted to the toner storing unit with its rear end received in the bore. The black container is provided with a spiral ridge on the inner periphery thereof for conveying the toner, and a toner outlet at one end of its circumferential wall. The toner outlet corresponds to a toner inlet formed in the hopper portion. When the developing unit and toner storing unit are rotated integrally, the black toner in the container is conveyed to the outlet and then dropped into the inlet of the hopper portion by gravity.
In Prior Art 4, each toner container should be replaced when it runs out of the toner. However, because the time when the toner is used up differs from one container to another container, it is preferable that each container can be replaced independently of each other. In light of this, there has been proposed a revolver in which the toner storing unit is provided with mount portions each accommodating one end of the associated toner conveying means and causing its toner inlet to face upward when the associated developing chamber is brought to a developing position. A toner container is mounted to the respective mount portion with its toner outlet facing downward. In this condition, the toner in the container is capable of flowing into the mount portion via the outlet due to its own weight. This kind of revolver will be referred to as Prior Art 6.
In Prior Art 6, the structure of the mount portion is applied only to color toner containers; a mount portion of different configuration is assigned to a black toner container provided with a greater capacity than the color toner containers. Specifically, a hollow cylindrical black toner container is formed with a toner outlet at one end of its circumferential wall and inserted into a bore formed at the center of the toner storing unit. A hopper portion is formed in the toner storing unit and provided with a toner inlet facing the outlet. The hopper portion accommodates one end of the toner conveying means and has a toner storing space of certain size. When the black toner chamber is located at the developing position, one end of the toner conveying means is positioned at the bottom of the hopper portion. when the outlet of the black toner container is brought to a higher level than the inlet by the rotation of the toner storing unit, the toner flows from the container into the hopper portion due to gravity.
The prerequisite with Prior Arts 1 and 5 is that the edge portion of the outlet of the container and that of the inlet be held in close contact with each other at the end of the movement of the container, thereby preventing the toner from flying about. To meet this requirement, an elastic seal member is adhered to at least one of the two edge portions. In addition, the edge portions are so configured as to set up a predetermined contact pressure when the two edge portions align with each other. However, when the container is slid with the edge portion of the outlet closely contacting the wall of the mount portion, a heavy load acts on the sliding movement. Further, when the two edge portions sequentially align with each other during the sliding movement, the seal member or members wear easily due to excessive rubbing. These load and wear problems are also apt to arise with Prior Art 5 when the container is slid into or out of the mount portion.
Assume that the container is inserted into the mount portion and then rotated in the mount portion to bring the toner outlet thereof into alignment with the toner inlet, as in Prior Art 2. Then, it is necessary to maintain the edge portion of the outlet and that of the inlet in close contact so as to prevent the toner from flying about. This requirement will be met if an elastic seal member is adhered to at least one of the two edges, and if the configuration of the edges and the axis of rotation are so selected as to set up a desired contact pressure when the two edges are aligned. However, when the container is rotated with the edge portion of the outlet closely contacting the wall of the mount portion, a heavy load acts on the rotation. Further, when the two edge portions sequentially align with each other during the rotation, the seal member or members wear easily due to excessive rubbing. These load and wear problems are also apt to arise with Prior Art 5 when the black toner container is rotated.
The problem with Prior Art 3 is that part of the developer around the outlet of the container is apt to rush past the outlet due to the force of the rotation. This part of the toner remains in the container until the outlet again faces downward, resulting in a low discharging efficiency. This problem is also apt to occur with Prior Art 6 in which the containers are rotated together with the developing unit and toner storing unit, and each toner is dropped from the outlet of the container by gravity.
Prior Arts 3 and 5 have another problem that when the containers are not rotated for a long period of time, the toner is apt to aggregate. When the toner aggregates to form a mass of substantial size around the toner outlet, it stops up the outlet and cannot be discharged.
Prior Art 2 has the following problems. Assume that the outlet of the black toner container is brought to a higher level than the inlet and allows the toner to now from the container into the hopper portion due to its own weight. At this instant, despite that a space is still available in the hopper portion at a position remote from the inlet, the toner accumulating around the inlet is likely to obstruct additional toner from the container. Another problem is that when the toner should be replenished into the hopper portion during the course of usual image formation, the previously stated positional relation is apt to cause the replenishment to be short or to increase the image forming time. Specifically, during usual image formation, the replenishment is likely to be short because the container and hopper cannot be maintained at the toner replenishing position for a sufficient period of time. Increasing the period of time for them to stay at the replenishing position would increase the image forming time.